Field of the Invention
The invention relates to an inductive component for the attenuation of common mode and push-pull interferences in n lead systems with n.gtoreq.2 leads.
The propagation ratios of lead-bound interference must be considered when dimensioning EMC filters (electromagnetic compatibility). One must also differentiate between common mode and push-pull interference.
Push-pull interference propagates only along the connected leads, whereby in a two-lead system the interference current moves along one lead in the direction of potentially susceptible equipment while moving along the other lead back toward the interference source. The two interference currents are in push-pull and therefore such interference is called push-pull or symmetrical interference.
Parasitic capacitances in the interference source and potentially susceptible equipment or intentional connections to ground also result in an interference current in the ground loop. The interference current flows along the leads to the potentially susceptible equipment and flows back through the ground leads. The interference currents on the leads are in common mode, thus such interference is called common mode interference or asymmetrical interference.
Current-compensated inductors are used to attenuate asymmetrical interference. However, those inductances are not suitable for the attenuation of symmetrical interference, since the required leakage inductance is very low (.ltoreq.1% of the asymmetric components). In order to compensate for that ineffectiveness against symmetrical interference, additional inductances which are effective against symmetrical interference are employed. Examples include bar or toroidal core inductors with very low inductance due to the use of low-permeability cores. However, such solutions are relatively expensive. The power loss of such systems is also rather high.